1. Field of the Invention
The present invention is related to a radiographic image (hereinafter also referred to as a radiograph) conversion panel and a method for manufacturing the same.
2. Description of the Related Art
In earlier technology, so-called radiography in which silver salt is used to obtain a radiological image has been utilized. However, the method for imaging a radiological image without silver salt has been developed. That is, the method of imaging by a phosphor absorbing the radial ray transmitted through a subject in a phosphor, thereafter, excited by certain type of energy, and radiating radiological energy accumulated in the phosphor as fluorescence, is disclosed.
A concrete example of a radiographic image conversion method is known, in which a panel comprising and a photostimulable phosphor layer provided on a support (hereinafter also referred to as base material) is applied, and both of/either visible light and/or infrared light is used as excitation energy (see U.S. Pat. No. 3,859,527).
A radiographic image conversion method using a photostimulable phosphor of higher luminance and sensitivity has been developed. A radiographic image conversion method using a BaFX: Eu2+ system (X: Cl, Br, I) phosphor disclosed in JP Tokukaisho-59-75200A, a radiographic image conversion method using an alkali halide phosphor disclosed in such as JP Tokukaisho-61-72087A, and an alkali halide phosphor containing metals of Tl+ Ce3+, Sm3+, Eu3+, Y3+, Ag+, Mg2+, Pb2+ and In3+ as a co-activator disclosed in JP Tokukaisho-61-73786A and 61-73787A are the examples.
In late years, in analysis of a diagnostic image, a radiographic image conversion panel having higher sharpness has been required.
As a method for improving the sharpness, for example, attempts of controlling the shape of photostimulable phosphor itself have been made in order to improve sensitivity and sharpness.
One of these attempts is, for example, a method of using a fine quasi-columnar photostimulable phosphor layer deposited on a support having a fine concavoconvex pattern, which is disclosed on JP Tokukaisho-61-142497A.
Further, the following methods and the like are also proposed; as disclosed in JP Tokukaisho-61-142500A, a method of using a radiographic image conversion panel having a photostimulable phosphor layer in which the cracks of a columnar photostimulable phosphor deposited on a support having a fine pattern are further developed with shock-treatment; as disclosed in JP Tokukaisho-62-39737A, a method of using a radiographic image conversion panel having a photostimulable phosphor layer cracked from the surface side to be quasi-columnar pattern; and, as disclosed in JP Tokukaisho-62-110200A, a method of forming a photostimulable phosphor layer having pores onto a support by deposition, subsequently the pores developped to be cracks with heat treatment.
Furthermore, as disclosed in JP Tokukaihei-2-58000A, a radiographic image conversion panel having a photostimulable phosphor layer in which elongated columnar crystals having definite angle based on a normal line of a support is formed by a vapor phase deposition method.
Every one of these methods of controlling the shape of a photostimulable phosphor layer can remarkably increase the sharpness of the photostimulated luminescence image, because a photostimulable phosphor layer is formed pillar shape so that photostimulated excited light or photostimulable luminescence is restrained to diffuse horizontally (a light reflects repeatedly on interface of cracks (of pillar crystal) to reach the surface of a support).
In late years, a radiographic image conversion panel using alkali halide such like CsBr as a base material is proposed. Especially when Eu is used as an activator, the improvement of X ray conversion efficiency, which has not achieved before, is expected (JP Tokukai-2002-72381A).
However, a deposition method for forming a membrane is required to form a CsBr: Eu phosphor layer. A base plate and a vapor source are located with high accuracy in order to control the membrane thickness distribution. Thus highly accurate membrane thickness distribution is achieved.
There is a problem especially in CsBr:Eu that Eu is distributed unevenly in the base material because vapor pressure of Eu in a vacuum state and predominant dispersion of Eu by heat is predominant. As a result, the structure of a deposition device and a location of a base plate and a vapor source highly affect the homogeneity of activator in a phosphor layer (For example, JP Tokukai-2002-72381A, 2002-20742A and 2002-6092A).
It is required that a board material with high rigidity is applied as an evaporation base board in order to improve accuracy of film thickness.
A stainless steel represented by Fe—Ni—Cr, a glass practically used in liquid crystal display and the like are known as base material with high rigidity. However, in relation to a radiographic image conversion panel using photostimulable phosphor that are used for X ray in medical use, the desired performance is not obtained since X ray is radiated from base material side (the opposite side of the phosphor side). As a result, there is a problem that the rigidity and X ray absorption of base material are incompatible.
For these reasons, the improvement of the homogeneity of activator in a phosphor layer has been required in order to improve the luminance and the sharpness of a radiographic image conversion panel, which are demanded from a market.